Problem: Multiply.
Explanation: ${8}$ ${1}$ ${9}$ ${3}$ ${9}$ ${\times\vphantom{0}}$ ${9}\times {9}= {81}$ ${1}$ ${10}\times {9}+80}= {170}$ ${7}$ ${800}\times {9}+100}= {7{,}300}$ ${3}$ ${7}$ ${9}\times {30}= {270}$ ${7}$ ${0}$ ${10}\times {30}+200}= {500}$ ${5}$ ${800}\times {30}= {24{,}000}$ ${4}$ ${2}$ ${+\vphantom{0}}$ ${3}$ ${1}$ ${9}$ ${4}$ ${1}$ $31{,}941=819 \times 39$